1. Field of the Invention
The present invention relates to a shift register and an electronic device using the same.
2. Description of the Related Art
In an active matrix display device such as a liquid crystal display device (LCD) and an EL panel, a shift register is used as a driver circuit (scan line driver circuit and signal line driver circuit) for reducing the number of signal input terminals. A shift register is configured by a plurality of registers connected in series. A signal inputted in each register is transferred to a next register according to a clock signal.
In such a driver circuit, a transistor which forms a register in a shift register may be abnormal (or broken) by static electricity and the like. In such a case, a signal is not transferred to a register of lower stage than the abnormal register (or broken register), which causes a defect in display. Such a display device cannot be shipped as a product, thus manufacturing yield is reduced. In view of this, a redundant structure is employed in which a plurality of shift registers are connected in parallel so that a driver circuit can function normally even when a register in the shift register is broken (see Patent Document 1). In the case of connecting two shift registers in parallel, for example, when a register of one shift register is broken, a corresponding register of the other shift register can be used instead. Thus a driver circuit can keep operating normally.    [Patent Document 1] Japanese Patent Laid-Open No. 6-83286